This invention relates to the field of military ordnance and, in particular, to the field of large caliber cannons, as typified by artillery weapons, where recoil forces are of major concern in the overall design. More specifically, the invention pertains to muzzle brakes as applied to large caliber guns and cannons and to the use of these brakes in the control of recoil forces during firing.
Large caliber military weapons, of which the U.S. Army""s 155 mm Self-Propelled Howitzer (one example known and referred to herein as xe2x80x9cCrusaderxe2x80x9d) is an exemplary case, deliver heavy rounds at relatively high velocities to distant targets. Simple conservation of momentum considerations dictate that the weapons and their support platforms are subject to heavy recoil forces during firing and, hence, to the negative effects of the recoil. It is common practice to mitigate the recoil and, thus, reduce the forces acting on the support platform of the weapon by installing or integrating a so-called muzzle brake at or near the muzzle end of the gun. These reduced forces result in lighter cannon support structures, enhancing mobility and effectiveness.
A muzzle brake is a device used to reduce the momentum of the recoiling components of a gun or cannon when fired by diverting the flow of propellant gases to produce an impulse that counters the breech-directed recoil of the gun. In traditional forms the brake may include a series of baffles either perpendicular or nearly perpendicular to the cannon tube axis or, alternatively, may be implemented as an integral perforated tube that consists of a series of radial holes located in the muzzle region of the cannon.
The need for, and efficacy of, such a device may be understood by considering the following: When the weapon is fired, the propellant burns rapidly and expands in volume inside the cannon. The projectile is accelerated along the length of the barrel by the expanding gases and is ejected at high velocity (on the order of 1000 m/s) from the muzzle end of the barrel. The high pressure propellant gases, exerting pressures of thousands of pounds per square inch, follow the projectile and are expelled into the atmosphere at velocities equaling and even exceeding those of the projectile. The combination of the accelerated projectile and propellant gases exiting the muzzle of the weapon produces a large breech-directed recoil thrust that is transmitted to the support structure.
It is understood that the magnitude and temporal characteristics of the recoil directly affect the design and implementation of the support structure. By installing or integrating a muzzle brake to the weapon the magnitude of the recoil and the forces transmitted to the support structure can be reduced by diverting the propellant gases and taking advantage of the impulse that is generated.
The firing event can be analyzed in two general scenarios: with and without a muzzle brake. In the case where no muzzle brake is installed, the high pressure, high velocity gases exit the muzzle and expand into the ambient atmosphere, creating substantial thrust and, thus, contribute an appreciable bore-directed force that is subsequently transmitted to the gun""s support structure. In contradistinction, when a muzzle brake is installed, a different sequence of events ensures. The projectile, accelerating down the length of the barrel, passes the muzzle brake and continues to restrain the propellant gases in the axial direction. Consequently, the expanding, high pressure gases are diverted to the baffles or to the forward face radial holes that comprise the muzzle brake. The diverted gases exit through ports in the muzzle brake to produce an impulse-like thrust that counters the breech-directed recoil of the gun, thereby reducing the recoil and the force transmitted to the gun""s support structure.
Muzzle brakes have traditionally been implemented in two major types. The first is an integral, perforated brake. In this implementation, an array of radial holes is drilled into the existing barrel of the weapon, at or near the muzzle. As an example, the Crusader has 120 radial holes arranged in ten axial rows, each with twelve equally-spaced circumferential locations. Gases impinge on the forward faces of the radial holes and subsequently change direction, ultimately being expelled axisymmetrically and almost radially around the muzzle of the brake. The interaction between the gas and the brake results in a momentum that counteracts the recoil of the gun.
The gas dynamic efficiency, xcex2, of such a brake is 0.6 or less, meaning that the reduction in recoil is somewhat limited. The lack of efficiency is offset somewhat by the simplicity (i.e., no components are added to the design), ease of fabrication, low cost, low added weight and minimal length of the design. It should also be noted that due to the axisymmetric placement of the exhaust ports, a fraction of the propellant gas is expelled downward, producing what is known as a ground surface disturbance that may affect the weapons platform and the crew that is operating the weapon.
A second type of muzzle brake is the so-called xe2x80x9cGerman baffle.xe2x80x9d In this design, a small number of baffles (typically 1 or 2) is incorporated into a separate assembly that attaches to the muzzle end of the barrel. The baffles and gas exhaust ports of this design lie in the horizontal plane and, thus, gases are expelled laterally, that is, parallel to the plane of the local ground. Thus, this design avoids the ground surface disturbance associated with the perforated brake. Advantageously, the German brake has a gas dynamic efficiency, xcex2, that may approach or exceed 1, implying a strong reduction in force transmitted to the support platform. However, the increased efficiency is offset by the cost and complexity of the units along with the penalties paid in weight. In addition, the relative complexity of the German baffle increases stress concentrations in undesirable areas and increases its manufacturing costs, with reliance on complex castings to produce the final product.
These two types of devices exemplify the current state-of-the-art in muzzle brake design. Though the structures described above may have satisfied their intended purpose, there still remains an unsatisfied need for an improved muzzle brake that achieves the desired goals of increased gas dynamic efficiency without endangering the crew of the weapons platform, decreased production costs, ease of manufacturing and assembly, and flexibility/tenability, as well as reduced weight and length.
The radial venting baffled muzzle brake of the current invention addresses the forgoing need. It also meets the following criteria:
1. minimized weight;
2. ease of manufacture and assembly;
3. optimized gas dynamic efficiency balanced with crew and platform safety;
4. minimized size;
5. flexibility and tenability; and
6. optimized material stress distribution.
It is a feature of the present invention to minimize the weight, size and length associated with the muzzle brake while achieving and maintaining a rugged and reliable design. This is achieved by fabricating the brake from lightweight materials and employing a novel, high efficiency design.
In a preferred embodiment, the brake is manufactured from lightweight, surface-treated titanium. Furthermore, the design achieves its desired performance with a compact, multistage, axisymmetric implementation that further minimizes weight, length and overall size of the brake.
An integral first stage baffle allows for a smooth transition to the radial exit passages, thereby maximizing its efficiency. In addition, the design and implementation of the main body of the brake allows for a radially uniform muzzle exit nozzle and incorporates a radially uniform first stage baffle. Thus, the geometry of these features strongly and positively influence muzzle brake efficiency.
Furthermore, the fillet radii transition between the main body""s integral gas deflection baffle and the exit passages are carefully engineered to assure uniform stress distribution and structural integrity, while maximizing brake performance.
The second stage baffle of the multi-stage design also allows for a smooth transition to the radial exit passages, thereby maximizing its efficiency. In addition, the second stage baffle design also incorporates a radially uniform muzzle exit nozzle, which strongly influences muzzle brake efficiency.
Furthermore, the fillet radii transition between the baffle and the exit passage is designed to assure structural integrity while maximizing brake performance. One further advantage of the invention is the design""s uniformity of structure, which enhances stress distribution from firing loads and thereby allows the structure size to be reduced to optimize overall system weight.
Another feature of the present invention is to employ standard manufacturing and assembly techniques in the implementation of the brake. In the preferred embodiment individual parts display a high degree of cylindrical symmetry, allowing them to be produced with standard machine tools, and/or simple casting methods. For final construction, the individual parts are readily assembled with standard tools and in final installation the brake, simply threads onto the muzzle of the cannon barrel. The design and implementation of the preferred embodiment reduces the overall cost of the brake.
Yet another feature of the present invention is to increase the gas dynamic efficiency of the brake to a level that will not endanger the crew or the support platform for the weapon. A high gas dynamic efficiency, xcex2, estimated to exceed 1.2, is achieved by employing a two-stage baffle design with axisymmetric venting. This gas dynamic efficiency may be increased or decreased as required by altering certain physical characteristics including baffle size, baffle deflection angle, and gas exit area.
The present design improves upon the gas dynamic efficiency of traditional xe2x80x9cGerman Bafflexe2x80x9d type design by utilizing full axisymmetric gas expulsion to achieve optimized propellant gas exit passage area per unit length. Additional baffles (e.g., a tertiary baffle) can be added to the design to further increase the gas dynamic efficiency, xcex2, of the muzzle brake with minimal weight impact.
Still another feature of the present invention is flexibility and xe2x80x9ctunabilityxe2x80x9d of the brake. The secondary baffle (or baffles, in the most general case) may be easily installed and removed enhancing internal stowage for transportation by reducing the total payload volume. In fact, the brake may be efficaciously and safely operated with the second stage baffle removed. It is estimated that the brake can achieve a gas dynamic efficiency, xcex2, approaching 1.0 with no secondary baffle installed.
In addition, the second stage baffle is readily adjusted by changing the length and diameter of the standoffs that couple the secondary deflection baffle to the main body of the brake. In this manner, the brake may be adjusted to conform to the particular operating conditions of the weapon.
The foregoing and additional features and advantages of the present invention are realized by implementing a multi-stage baffle design with full radial venting of expelled propellant gases. The main body of the device comprises an internally-threaded, cylindrically shaped lug, a cylindrically symmetric gas baffle, and a plurality of gas exhaust ports which are arranged in such a manner as to take maximum practical advantage of available exhaust gas energy.
The main body of the muzzle brake is threaded onto an existing gun barrel and further secured with a key and collar arrangement to prevent loosening as a result of repeated use. A secondary gas deflection baffle may be secured to the main body of the muzzle brake by means of a plurality of cylindrical standoffs and an equal number of nuts. The axisymmetric secondary baffle is installed a predetermined distance from the first, to optimize braking efficiency. The intervening spaces between the standoffs serves secondary gas exhaust ports.
The muzzle brake of the current invention is easily produced using conventional manufacturing techniques, easily assembled with standard tools, achieves high gas dynamic efficiency without endangering the weapons platform or the gun crew, and is both lightweight and compact. The axisymmetry of the design prevents unbalanced forces and moments from being applied to the barrel of the cannon and, furthermore, assures high efficiency for the design. In particular, the gas dynamic efficiency, xcex2, of the invention exceeds that of the traditional German baffle and doubles the gas dynamic efficiency, xcex2, of a standard, integral perforated brake.